The present invention relates to a supporting cross-beam for vacuum hold-down tables designed to hold in place panels, in particular wooden panels. Machinery for the machining of wooden workpieces (in the present text wooden workpieces include items such as wooden boards, sections and panels used in the mass production of articles for industry or furnishings) currently have various types of tables designed to support and hold in place the workpieces so that precision machining can be effected on them. Of interest in the present invention are the type equipped with suction cups, on which the workpiece is held in place by means of a vacuum created by air suction.
Such tables are generally defined by a series of cross-beams, each supporting a plurality of vacuum hold-down tables which form the actual support surface for the workpieces. The cross-beams are parallel to one another and can be moved manually along the machine's longitudinal axis (usually called the X-axis) together with a pair of bilateral fences (using a manual locking and release system. Associated with each cross-beam are one or more vacuum hold-down tables which can be moved along the machine's transversal axis (usually called the Y-axis) by the operator, again manually. Each table consists of a horizontal support surface, upon which a seal is fitted. The configuration of the seal may vary according to hold-down requirements on certain areas of the workpiece, but it is always a single piece. The seal is inserted between the workpiece and the support surface, providing a vacuum in the desired zone by means of the suction produced by the relative pneumatic system located beneath the table, so as to hold down the workpiece securely.
However, these tables have several disadvantages, caused mainly by the pneumatic suction system which, in order to obtain optimum holding of the workpiece above, must have a plurality of pipes, one for each cross-beam and one for each vacuum hold-down table. The first pipes extend from the machine support base, the normal location of the suction means, and lead to the relative cross-beam, whilst the second pipes extend from the relative support table to a fitting which unites them with the corresponding first pipes. All pipes must also be long enough to allow the safe movement of both the cross-beams and the vacuum hold-down tables within the "ranges" of movement. Considering that a medium sized machine has more than one cross-beam, upon which at least two vacuum hold-down tables are fitted, a considerable number of pipe units are required in order to obtain normal air suction from the vacuum hold-down tables.
This pneumatic network normally used therefore requires many items of equipment (pipes and relative control systems) and occupies working space on the machine which, as a result, has only limited open areas without components. The disadvantage of this is that it is impossible to rapidly and safely clean away the shavings produced during machining, which usually fall in the areas beneath the vacuum hold-down tables. This difficulty arises due to the number of pipes and all of the electrical cables necessary for machine functioning.